This invention relates generally to a method of downhole turbine operation in which substantial amounts of the power needed for the turbine operations are supplied from in situ forces. Because the supply of power for downhole operations from surface power sources is both difficult and expensive, significant economic benefits will be expected to derive from the use of the said in situ forces. The forces to be used arise from gases which can be released from fluids surrounding a well--such released gases can be expanded as they flow toward lower pressures at the earth's surface, and such expansion can be made to do useful work.
Brines and petroleum at high pressures are known to dissolve substantial amounts of valuable gases; for examples, hydrocarbon gases (e.g., methane, the principal component of natural gas) and carbon dioxide (a gas with numerous uses such as for dry ice or for tertiary recovery of petroleum) are frequently present in commercially valuable quantities around wells in oil and gas fields. Such dissolved gas can be substantially released from high-pressure solution by reducing the pressure above brine or petroleum, and if the brine or petroleum is brought to the surface the dissolved gases usuallly are recovered. However, commercially practical means to circulate fluids underground so that their dissolved gases can be recovered in a well by pressure reduction usually are not available with current technology; a major obstacle to suitability of technology has been the expense and difficulty of supplying surface power to underground uses, expenses and difficulties which could be circumvented by devices applying the methods of the present invention.
Similarly, brine at elevated pressures and temperatures can release steam if the pressure is reduced over the brine. If such brine could be circulated from a deep, hot formation, into a well where the pressure could be reduced, and back into a disposal formation, then steam could be released from the brine and be delivered to the surface. Such steam would be a valuable source of fresh water as well as a source of heat.
Likewise, brines or petroleum in natural formations underground may entrap bubbles of gas comprising methane, other hydrocarbons, carbon dioxide, or combinations of these and other gases. Such natural entrapment may be substantially increased by man's actions, particularly when hydrocarbons are commercially produced from wells. Here intruding brine may trap droplets of petroleum or bubbles of gas; temperature changes during gas production may result in gas condensation and entrapment in gas wells; or too large pressure gradients may produce channeling which bypasses materials which one would like to recover. As a consequence, wells which have watered out to uselessness often still contain as much as half of their original hydrocarbon content. Self-powered means to circulate more brine through the formations just discussed would offer the possibility of recovering considerably more of the entrapped hydrocarbons. Such self-powering is offered by the present invention.
Self-powering by in situ forces is claimed in prior art by Elliott, et al., U.S. Pat. No 4,262,747, issued Apr. 21, 1981. In that patent, for example, gas lift is used to raise brine into a standpipe, and the head of the standpipe is used to force the reinjection of brine from which the dissolved natural gas has been removed, thereby downhole accomplishing brine circulation and gas removal by downhole forces. However, this and all other prior art has failed to identify certain novel uses of already commercialized pumps called centrifugal pumps or turbine pumps by their manufacturers; these novel uses are described further in the next paragraph and are the subject of the present patent. Further use of downhole forces to power pumps is claimed in patents, not yet issued, by Elliott, et al., (U.S. Pat. No. 4,376,462 to issue Mar. 15, 1983, and No. 4,377,208 to issue Mar. 22, 1983), but these patents also fail to identify the novel use of centrifugal pumps or turbine pumps as follows.
"Centrifugal turbines" is the phrase we will use instead of centrifugal pumps or turbine pumps because, under the present invention, the devices are used both as substantially self-powered motors and as conventional pumps. These centrifugal turbines are here used in a novel and unobvious way as downhole motors powered by the expansion of gas in gas-liquid mixtures as these mixtures move toward lower pressures. These lower pressures toward which the gas expands will usually be established by a gas path toward lower pressures at the earth's surface; substantially pure, spent brine (i.e., brine with its gas largely removed and without important amounts of petroleum droplets) will usually be pumped into a disposal formation without ever moving to the earth's surface; petroleum, or petroleum-water mixtures which do not separate readily, will usually be pumped to the earth's surface for recovery. Centrifugal turbines are especially useful for motor operations such as these in which expanding gas imparts velocity, momentum, and kinetic energy to liquids in gas-liquid mixtures--specifically, the design of the stages of gas-liquid turbines allows substantially continuous flow through a series of these stages, and, as the stage pressures are lower (i.e., are closer to atmospheric pressure), the velocities of the liquid become larger and larger and the kinetic energies available to the motor to allow it to do work also increase, with the square of the velocity. As compared with most other types of pumps used downhole, centrifugal turbines are particularly well suited for motor operation as just described. Note, however, that centrifugal turbines and other downhole pumps were designed for use as pumps, not as motors: All downhole pumps being built commercially are designed to be powered from the earth's surface.
Because centrifugal turbines can be worked before gas-liquid separation, they can be made to do work at all pressures from high formation pressures to near atmospheric pressures--this large operating range is a great advantage for downhole-motor use.
Gas turbines, like centrifugal turbines, have the advantage that they can accommodate some liquid, and their use is claimed along with centrifugal turbines under the present invention. However, gas turbines will normally be used only after gas-liquid separation. Therefore, in a practical sense, these gas turbines cannot be worked at high formation pressures.